Linear stage systems are utilized for precision motion in linear directions. Linear stage systems are commonly used in manufacturing processes, such as semiconductor manufacturing. A linear stage system may be used to position a silicon wafer at a specific position so that a mask image is in focus on the wafer surface. In such photolithography applications focus is critical and is accomplished by ensuring that the surface of the wafer is in a precise position for best possible focus. Other applications for linear stage systems may arise in testing semiconductors where a wafer must be lifted against a set of probes. Once again vertical positioning of the wafer is critical since overdriving the probes may damage them.
One common linear stage system is a Z wedge design used to create motion in the Z, or vertical, direction. Many versions of Z wedge designs exist but this design inherently has many errors associated with it. The motors typically drive in a horizontal dimension and bearings constrain the stage such that motion results in a vertical direction. Bearings always have some dimensional error or parallelism errors that are included in the motion. Additional errors are induced by machining accuracy errors, which are greater than normal for the angular surfaces required of such a design. Often the encoder measures horizontal motion and the results are calculated into the resulting Z motion. This calculation requires assumptions that add to the Z linear accuracy error.
Other Z stage designs use mechanical bearings with encoders and motors oriented vertically. This eliminates some of the errors with the Z wedge design but mechanical bearings still induce errors and are largely dependent on machined surfaces. Additionally stages in this orientation also tend to be large dimensionally in the Z direction.